Method for controlling an injection valve

ABSTRACT

A method for controlling an injector is described, where the trigger signal (Ua) for the actuator is controlled as a function of the amplitude and the duration. The actuator, using an hydraulic coupler, actuates a control valve which, at a low voltage, operates in a ballistic mode and opens up an opening cross-section to an inlet channel (ZK). The opening cross-section (8) becomes smaller with increasing trigger voltage (Ua), and the fuel quantity to be injected increases. The control valve (5) is brought from ballistic mode to nonballistic mode via the amplitude and duration of the trigger voltage (Ua). The delivery duration (FD) and the amplitude of the trigger voltage (Ua) are tuned to each other so that one or several jumps may occur, during which a switch is made from one voltage value (Ua) to another voltage value (Ua), and from one delivery duration to another delivery duration (FD). The method is preferably used in a unit injector system such as is used in direct injection. A piezoelectric element is preferably used as an actuator (2).

BACGROUND INFORMATION

[0001] The present invention is based on a method for controlling aninjector via which a specified quantity of fuel is injected into thecylinder of an internal combustion engine, according to the definitionof the species of the main claim. Methods of fuel injection into aninternal combustion engine, in particular in direct injection, arealready known. For example, in a unit injector system (UIS), a controlvalve is controlled by a magnetically operated actuator in step with atrigger signal for injecting, under high pressure, a specified quantityof fuel into the combustion chamber of the engine. This creates theproblem of also being able to inject the smallest possible controllablequantities of fuel. These small quantities are on the order of magnitudeof up to 2 mm³ for all operating conditions. In the case of the knownmagnetically controlled actuators, these small quantities cannot beachieved, especially when the engine runs at high rotational speeds,since the control valve is only adjustable to a limited extent inintermediary positions between the open and closed states. Piezoelectricactuators, on the other hand, control the injected quantity only via aconstant opening cross-section, formed between the control valve and itsseat in the intake channel.

ADVANTAGES OF THE INVENTION

[0002] The method according to the present invention for controlling aninjector having the characteristics of the main claim has the advantageover the related art that, for controlling the fuel quantity, thetrigger signal for the actuator is adjustable in amplitude as well as induration. This has the advantage that it is possible to inject a small,precisely-metered fuel quantity not only at low RPMs and low load. It isalso possible—in particular when using a piezoelectric actuator—toinject the quantity of fuel to be injected in a targeted manner and, asa function of engine load and rotational speed, in a defined manner, viathe amplitude of the trigger voltage as well as the duration of theapplied control signal. It is particularly advantageous that it ispossible to also consider parameters containing engine-related,emission-relevant, and drive-specific components.

[0003] The measures described in the dependent claims make advantageousrefinements of and improvements on the method described in the mainclaim possible. It is considered especially favorable that the triggersignal is initially selected in such a way that the control valve is inballistic mode and therefore clears the opening cross-section of theintake channel. If the injection quantity is to be increased, theamplitude of the trigger signal is simply increased as well, withinitially the same delivery duration, so that the opening cross-sectionof the inlet channel narrows. During this phase, the duration of thetrigger signal remains constant.

[0004] To further increase the injection quantity, the control valve isadvantageously switched to nonballistic mode. This makes is possible toachieve further increases in the quantity of fuel to be injected, evenafter the switchover to nonballistic mode.

[0005] It is also considered advantageous to increase the duration ofthe delivery until the quantity of fuel to be injected is larger thanthat which can be achieved with a closed control valve and short triggersignal. In this case, in order to achieve a favorable engine behavior,it is possible to provide at least one jump in the delivery duration andamplitude of the control signal in order to achieve a change in thedetermination of the quantity.

[0006] This makes it possible to select the maximum amplitude of thecontrol signal with only one jump. Further increase in the injectionquantity is then achieved by extending the duration of the delivery.

[0007] In an alternative embodiment, several jumps may be used,increasing the trigger voltage incrementally and adapting the deliveryduration to the specified injection quantity with each jump.

[0008] It is also possible to advantageously increase the trigger signalup to its maximum value, with the control valve resting on the valveseat and sealing off the opening cross-section. In this case, furtherincrease in the trigger signal does not result in an additional increasein the delivery quantity. Rather, the latter is achieved by extendingthe duration of the delivery.

[0009] An advantageous application of the method uses a piezoelectricactuator, which is used in particular in a direct-injection system.

DRAWING

[0010] One embodiment of the invention is shown in the drawing anddescribed in more detail below. FIG. 1 shows an injection valve having aunit injector; FIG. 2 shows a first diagram having characteristic curvesfor injection quantities as a function of the delivery duration andvoltage; FIGS. 3a and 3 b show characteristic curves for the triggersignal; FIGS. 4a, 4 b and 4 c show additional characteristic curves forthe trigger signal; FIG. 5 is a second diagram having discontinuouscharacteristic curves for the triggering signals in the injectionquantity characteristics map, and FIGS. 6 and 7 show alternativecharacteristic curves for the trigger signal.

DESCRIPTION OF THE EMBODIMENTS

[0011]FIG. 1 is a sectional view of injector 1 having a unit injectorsystem (UIS). In this known unit, pump unit 6 is actuated by a plunger Aand generates a high injection pressure PI in a high-pressure channel.The fuel to be injected is in the high-pressure channel and capable ofbeing injected—at a corresponding pressure—into the cylinder of aninternal combustion engine (not shown) via a nozzle needle 3. The waythis injector valve functions is known per se and, therefore, only itsbasic functions are explained. The central element is a control valve 5,located in the high-pressure area and, depending on its position inrelation to valve seat 7, forms an opening cross-section 8, via whichmore or less fuel is able to flow into an inlet channel ZK that isformed between a connector Z and opening cross-section 8. In this inletchannel ZK, there is a corresponding low pressure (inlet pressure PO).Control valve 5 is actuated—via an hydraulic coupler 4—by an actuator 2that receives a trigger voltage Ua via terminals + and −. Actuator 2essentially has a piezoelectric element that performs linear expansionas a function of trigger voltage Ua. Depending on the change in lengthof actuator 2, control valve 5 is moved via hydraulic coupler 4 andachieves any desired intermediate position in the so-called ballisticmode. If, on the other hand, control valve 5 rests on valve seat 7, theso-called nonballistic mode is achieved where the opening cross-section=0.

[0012] The present invention is now based on the idea of configuringcontrol valve 5 by varying the amplitude and trigger duration of triggersignal Ua in such a way that in every operating state of the internalcombustion engine the desired fuel quantity to be injected is achievedby the position of control valve 5 and its dwell time in one position.It is assumed here that at a maximum value of trigger signal Ua, i.e.the maximum trigger voltage Umax, control valve 5 rests firmly on valveseat 7, causing the opening cross-section to be 0. Therefore, a fuelquantity is injected as a function of delivery duration FD, which may beexpressed in degrees per crank angle of the crankshaft or camshaft.Alternatively, it is possible to specify an injection duration on a timescale. In ballistic mode, on the other hand, the injection quantity isreduced—always measured at constant injection duration—because,depending on the position of control valve 5 over opening cross-section8, more or less fuel may flow into inlet channel ZK in the direction Z.By optimally controlling the position of control valve 5 and alsodelivery duration FD, which depends on the length of trigger signal Ua,it is possible to control the quantity of fuel to be injected. It isadvantageous here that all operating conditions or requirements for theexhaust gas or driving behavior are capable of being taken intoconsideration.

[0013]FIG. 2 shows a first diagram containingdelivery/injection-quantity characteristics, based on which it ispossible to build an initial embodiment for trigger sequences. Deliveryduration FD is plotted on the x axis, and injected fuel quantity Q isplotted on the y axis. The delivery duration is preferably stated inangular degrees of crankshaft KW.

[0014] The effect on delivery quantity Q is shown by the various curves.Curve 1, for example, starts at Q=0 mm³ delivery quantity, with thedelivery duration initially held constant at value x° KW. Here, controlvalve 5 is in ballistic mode, i.e. opening cross-section 8 initially isat its highest value, so that delivery quantity Q=0. With increasingcontrol voltage Ua, opening cross-section 8 becomes smaller, so thatdelivery quantity Q increases along curve 1 until, at the break point,maximum value Q2 is reached initially. Here, control valve 5 rests onvalve seat 7 and has inlet channel ZK closed. A further increase of fuelquantity Q to be injected is now only possible by increasing deliveryduration FD along the linear portion of curve 1. Curve 4 starts withdelivery quantity Q1 and enters the right branch of curve 1 or 2 withincreasing delivery duration FD. Q1 is the delivery quantity at U_(max),i.e. when control valve 5 rests on valve seat 7 and openingcross-section 8 is closed (=0). Q1 here is significantly higher than thesmallest required quantity. The same applies to Q I in FIG. 5 as well.

[0015] In ballistic mode, for example, control valve 5 is held at anintermediate position, according to straight lines 2 and 3, by voltageU1 or U2, so that more or less fuel is able to flow from thehigh-pressure channel to inlet channel ZK. Delivery quantities Q aregiven accordingly. For example, straight line 2 shows, in the case oftrigger voltage U1, that the delivery quantity increases linearly withdelivery duration FD. Straight line 3 shows that, at higher triggervoltage U2, delivery quantity Q also increases, since a higher voltagecauses opening cross-section 8 to become smaller. If, for example,during ballistic mode, voltage U1 is selected for the left branch ofcurve 2, the delivery quantity increases up to value Q3 for deliveryduration x° KW. With increasing trigger voltage Ua and constant deliveryduration FD, delivery quantity Q now increases, as shown by the verticalpartial curve, until value Q2 is reached. Afterwards, delivery durationFD is again increased, so that curve 2 runs the same way as curve 1. Inthis branch, nonballistic mode is again in effect. Transition tononballistic mode takes place at delivery quantity Q2 whose valuedepends on the actuator type, among other things.

[0016] The characteristic curves for trigger signal Ua according toFIGS. 3a and 3 b show trigger cycles for the transition from ballisticto nonballistic mode via an increase in voltage. Here, FIG. 3a shows thetrigger sequence for curve 1 of FIG. 2 along with the ballistic area. AsFIG. 3a further shows, trigger voltage Ua is increased stepwise until,at instant t1, fuel delivery begins for injection. It is possible tovary voltage Ua according to the broken-line curves in FIG. 3a, withdelivery duration FD remaining constant. After disconnection, controlvoltage Ua drops to the value of 0 according to the slope shown.

[0017] In FIG. 3b, on the other hand, delivery duration FD isselectively increased when reaching maximum voltage Umax, resulting inthe broken-line characteristics in this case. This applies to thenonballistic mode of curve 4 in FIG. 2.

[0018]FIGS. 4a through 4 c show additional characteristics for thetrigger signal. For example, according to FIG. 4a, control valve 5remains in ballistic mode when trigger voltage Ua=U1. Delivery durationis now extended from 0° to x° KW according to the broken-linecharacteristics or a corresponding period of time (left branch of curve2 in FIG. 2). Now, if delivery duration FD reaches value x° KW, forexample, delivery quantity Q increases as shown by the vertical branchof curve 2 in FIG. 2, because control signal Ua was increased as shownin FIG. 4b. Control valve 5 now firmly rests on valve seat 7 at Umax.According to FIG. 4c, delivery duration FD is now extended as shown bythe broken-line characteristics. Delivery quantity Q changescorrespondingly along the right partial curve 2 in FIG. 2.

[0019] Similar behavior applies to control voltage Ua=U2.

[0020]FIGS. 5 through 7 show, in another embodiment, how coordinatingdelivery duration FD and increase in voltage make it possible to preventintersections by inserting one or several jumps. FIG. 5 shows a seconddelivery-quantity diagram having several jumps in the trigger signals,where delivery quantity Q is plotted on the y axis against deliveryduration FD on the x axis. Curve a is a nonlinear curve having a jump.For example, assuming delivery duration FD=0°, delivery duration FDincreases along curve a (with trigger voltage U₁) until durationFD=value x°. In this position, the amplitude of trigger voltage Ua aswell as delivery duration FD are changed, while the delivered fuelquantity remains the same. For example, the voltage is set to themaximum, and the delivery duration is limited to value y°. An increasein delivery quantity Q is now possible only along additional curve a1if, in turn, delivery duration FD is increased.

[0021] In an alternative embodiment of the present invention, severaljumps are possible instead of just one jump. This is represented bycharacteristics b. Delivery duration FD is switched between values x°and z°. If, for example, the delivery duration reaches value x°,corresponding to voltage U1, an upward switch is made to control voltageU2 and, at the same time, the delivery duration is reduced to value z°.Now, delivery duration FD is again increased until value x° is reachedagain. At this point, another switch is made—as shown in characteristiccurve b—to the next higher voltage U3 having delivery duration z°. Now,delivery duration FD is again increased until value x° is reached. Now,a jump back is made to characteristic curve a1, as was shown in theprevious example. This characteristic curve a1 corresponds to themaximum trigger voltage U_(max) which is permissible for the selectedactuator type It must be noted, however, that the switch, or jump, fromFD and Ua always takes place at points of the same delivery quantity Q.The number of jumps is freely selectable. Many small jumps result in abetter tolerance and engine behavior than few large jumps.

[0022]FIGS. 6 and 7 show corresponding voltage curves for triggervoltage U1 for ballistic mode. According to FIG. 6, control voltage Uais increased until delivery starts at instant t1. Now, delivery durationFD is extended as shown by the broken-line curve. If—as in FIG.7—trigger voltage Ua reaches maximum value Umax, nonballistic mode is ineffect, during which the delivery duration is extended according to thebroken line.

What is claimed is:
 1. A method of controlling an injectionvalve/injector (1) to inject a specified fuel quantity into the cylinderof an internal combustion engine, the injector (1) having a controlvalve (5) that is triggered by an actuator (2) and opens or closes aninlet channel (ZK) for the excess fuel, wherein the trigger signal (Ua)for the actuator (2) is variable in amplitude and/or duration forcontrolling the fuel quantity.
 2. The method according to claim 1,wherein the trigger signal (Ua) for a small injection quantity is so lowthat the control valve (5) is maintained in ballistic mode having anopening cross-section (8) for an inlet channel (ZK), and for increasinginjection quantities, the trigger signal (Ua) is increased in order tonarrow the opening cross-section (8) of the inlet channel (ZK).
 3. Themethod according to claim 1, wherein the trigger signal (Ua) isincreased until the control valve (5) goes into nonballistic mode andcloses the inlet channel (ZK).
 4. The method according to one of thepreceding claims, wherein the duration of the trigger signal (Ua), i.e.,the duration of the delivery (FD) is extended in order to increase thefuel quantity to be injected.
 5. The method according to claim 4,wherein the delivery duration (FD) is extended until the injected fuelquantity is larger than the quantity attainable with closed controlvalve (5) and a short trigger signal (Ua) having a high amplitude. 6.The method according to claim 4 or 5, wherein at least one jump is made,during which the delivery duration and the amplitude of the triggersignal (Ua) are changed simultaneously.
 7. The method according to claim6, wherein the maximum amplitude of the trigger signal (Ua) is selectedwith only one jump, and the delivery duration (FD) is changed in orderto determine the injection quantity.
 8. The method according to one ofthe preceding claims, wherein the trigger voltage for the fuel quantityto be injected occurs in several jumps, where the delivery duration andthe amplitude of the trigger signal (Ua) are changed with each jump. 9.The method according to one of the preceding claims, wherein theamplitude of the trigger signal (Ua) and the delivery duration (FD) arechanged until the trigger signal (Ua) has reached its maximum value(Umax).
 10. The method according to claim 9, wherein a further increasein quantity is achieved by extending the delivery duration (FD).
 11. Themethod according to one of the preceding claims, wherein a piezoelectricelement (2) is used as actuator.